The present application relates generally to power distribution systems and, more particularly, to methods of operating power distribution systems including a communication network.
Known power distribution systems include a plurality of switchgear lineups including circuit breakers that are each coupled to one or more loads. The circuit breakers typically include a trip unit that controls the circuit breakers based upon sensed current flowing through the circuit breakers. More specifically, the trip unit causes current flowing through the circuit breaker to be interrupted if the current is outside of acceptable conditions.
Some known circuit breakers are programmed with one or more current thresholds (also known as “pickup” thresholds) that identify undesired current levels for the circuit breaker. If a fault draws current in excess of one or more current thresholds for a predetermined amount of time, for example, the trip unit typically activates the associated circuit breaker to stop current from flowing through the circuit breaker. However, in power distribution systems that include a plurality of circuit breakers, a typical arrangement uses a hierarchy of circuit breakers. Large circuit breakers (i.e., circuit breakers with a high current rating) are positioned closer to a power source than lower current feeder circuit breakers and feed the lower current feeder circuit breakers. Each feeder circuit breaker may feed a plurality of other circuit breakers, which connect to loads or other distribution equipment.
A fault may occur anywhere in the circuit breaker hierarchy. When a fault occurs, each circuit breaker that has the same fault current flowing through it may detect different amounts of fault current as a result of varying sensor sensitivities and/or tolerances. When the fault occurs, the circuit breaker closest to the fault should operate to stop current from flowing through the circuit breaker. If a circuit breaker higher in the hierarchy trips, multiple circuits or loads may unnecessarily lose service.
To accommodate for the varying tolerances and to ensure that multiple circuit breakers do not unnecessarily trip based on the same fault current, the current thresholds of at least some known circuit breakers are nested with each other to avoid overlapping fault current thresholds. In some other known systems, circuit breakers in a lower tier send coordination or blocking signals to higher tier circuit breakers upon detection of a fault current and the upper tier circuit breakers' operation is coordinated with the operation of the lower tier circuit breaker in response to the blocking signal. The signals are typically transmitted over a dedicated connection between a blocking signal output in the lower tier circuit breaker and a blocking signal input in each upper tier circuit breaker with which the lower tier circuit breaker must be coordinated. The blocking/coordination signals are typically a simple binary (on/off) signal in which the presence of a voltage indicates a blocking signal and the absence of a voltage indicates the absence of a blocking signal. Some known systems incorporate a third signal, such as a periodic pulse, to add an additional indication, such as to confirm there is no blocking signal but the connection between circuit breakers is still functioning. Such known systems do not provide any additional information from the lower tier circuit breaker to the upper tier circuit breakers in connection with the blocking signal.
In certain system topologies, circuit breakers known as ties, which connect distribution busses in the same tier of a system with multiple sources supplying multiple busses, cannot detect fault current direction. The trip unit in the tie does not know whether current is flowing through the tie from right to left or left to right. When a fault occurs the tie must send a blocking signal to upper tier devices on all connected sources. This results in the undesirable operation that all source devices are blocked when it may otherwise be desired that at least one of them not be blocked.
At least some known power distribution systems include circuit protection devices operable in at least two protection modes: a normal protection mode and a maintenance mode. In the normal protection mode, current thresholds (also known as “pickup” thresholds) that identify undesired current levels are set to protect equipment, such as a load or other protection devices. The maintenance mode is commonly activated by a person when the person will be interacting with a load or protection device downstream (in a lower tier) from a protection device. In the maintenance mode, the protection device's settings are adjusted to make it more sensitive to undesired current levels and, if possible, decrease the amount of time needed by the protection device to react to an undesired current level. Thus, a protection device is easier and/or quicker to trip when the maintenance mode is enabled. The maintenance mode of a protection device is typically manually enabled and disabled by a person. Failure of a person to enable a maintenance mode in a protection device in some known systems increases the danger to a person working downstream from the protection. Failure to return the protection device from the maintenance mode to the normal protection mode may increase the likelihood that the protection device will trip unnecessarily.
At least some known power distribution systems include circuit protection devices with ground fault detection capabilities. A circuit protection device that disconnects a circuit when it detects that electric current is not balanced between conductors, for example between a line conductor and a neutral conductor, may be referred to as a residual current device (RCD). RCDs include, for example, ground fault circuit interrupters (GFCIs), ground fault interrupters (GFIs), appliance leakage current interrupters (ALCIs), residual-current circuit breakers with overload protection (RCBOs), and electronic residual-current circuit breakers with overload protection (eRCBOs). Ground fault detection capabilities of a circuit protection device are often controlled based only on data that is collected directly by the circuit protection device without full knowledge concerning operation of other circuit protection devices or other portions of the power distribution system.
Some known power systems utilize relatively simple circuit protection devices in connection with a centralized controller. The centralized controller receives data from sensors disposed throughout the power distribution system. The centralized controller commands and coordinates operation of the various circuit protection devices in the power distribution system based on the sensed data.